Effects of Searsia lancea hydrochar inclusion on the mechanical properties of hydrochar/discard coal pellets

Abstract

The utilization of biomass as a solid fuel for co-firing has received great attention from boiler manufacturers as a clean coal technology (CCT) option. This research aimed to produce biocoal pellets, as a clean energy fuel, using hydrochar from trees planted to rehabilitate acid mine drainage (AMD) water and fine coal discards. The hydrochar was synthesized by hydrothermal carbonization of Searsia lancea harvested from AMD-contaminated land at a temperature of 280°C and a residence time of 90 minutes. It was blended with discard coal (-1 mm) at ratios of 25% and 50% hydrochar to produce different forms of solid pelletized biocoal (BC). The physicochemical and mechanical properties of each of the biocoal pellet blends were determined. The 100% hydrochar had the highest calorific value of 29.99 MJ/kg, while the raw discard coal had a calorific value of 16.73 MJ/kg. The ash content decreased from 42% in the discard coal to 25% in the blend of 50% coal and 50% hydrochar biocoal pellets. Biocoal pellets comprising 25% hydrochar and 75% discard coal (BC25HC/75COAL) displayed the best mechanical properties (compressive strength 3.06 MPa) of all the fuels, but the physicochemical properties were inferior to the BC50HC/50 COAL pellets. This research has demonstrated that hydrochar synthesized from a tree species planted for hydraulic control of AMD has the capability to act as a binder for improving the mechanical properties and energy characteristics of fine discard coal.

Co-firing of high-ash discard coal and refuse-derived fuel - ash and gaseous emissions

“…The RDFs had a low fixed carbon (6 -9%) and ash (6.66%−11.11%) content, while the coal discard had an ash content of 41.95%. The coal discard used in this study can be categorized as a commercial low-grade (grade D III) coal due to its calorific value of 16.73 MJ/kg (Setsepu, Abdulsalam, and Bada, 2021). Furthermore, the fixed carbon content (35.83%) is close to that of coals sampled from three commercial South African coalfired plants (40.3−46.8%) reported by Rautenbach et al (2019).…”